The Short Life and Long Times of Mrs Beetonby Kathryn Hughes544pp, Fourth Estate, £20

We all know about Mrs Beeton - a dragon in black bombazine, presiding with iron control over her bustling underlings in the steamy cavern of a Victorian kitchen, conjuring up hefty haunches of roast beef and a parade of solid steamed puddings. Well - no. The real Isabella Beeton wrote her massive Book of Household Management at 21. She was a fashionable and modern young woman, unconventional in her upbringing and opinions, with rather more interest in clothes than in cooking. She worked as a journalist alongside her publisher husband, and died in 1865 of puerperal fever, almost certainly caused by the failure of the attending doctor to wash his hands before delivering her fourth child. She was 28.

If Beeton was not what we think she was, neither was her book. Household Management is popularly seen as extravagant ("take 12 dozen eggs") or as representing a lost rural way of life ("first catch your hare"). In fact, it is neither. Although the book does contain a few conspicuously extravagant recipes, if anything it errs on the side of frugality, with many pages devoted to plain family dinners and the use of leftovers.

Beeton wrote at a time when the industrial revolution was in full swing - a generation at least after the massive shift of population from the countryside to the towns. The rural economy in which most people produced their own food was already lost by the time she embarked on her book, and she is almost as nostalgic for that old connection to the land as we are today. And despite their frequent attribution to her, those lines about eggs and hares were never written by Beeton - a detail that serves to demonstrate the persistent mythmaking to which her book has been subject.

Kathryn Hughes's excellent biography has a dual purpose: to flesh out the facts of Beeton's brief life, and to explore the vibrant afterlife of her book. Hughes, whose George Eliot: The Last Victorian won the James Tait Black prize for biography, has had untrammelled access to the diaries and letters of Beeton and her husband Samuel - much of which material has never before available to biographers or food historians. The result is a fascinating reconstruction, which shows Isabella and Sam as in some ways absolutely typical of a certain new stratum of the mid-Victorian middle classes - thrusting, entrepreneurial and upwardly mobile: only a couple of generations from the servant class, and one from the sort of people who lived "over the shop".

Yet in other ways they were highly unusual. In the course of her marriage, Isabella became a working journalist, progressing from translating French novels for serialisation in Sam's Englishwoman's Domestic Magazine to editing the Book of Household Management (she notably never referred to herself as author, a tacit acknowledgment that the book was largely a scissors-and-paste job). By 1860 she had also become the editor of the magazine, and for two years, leaving her young child at home, she commuted daily into the city with Sam from their home in Pinner - no doubt, as Hughes remarks, cutting a curious figure in the otherwise exclusively male surroundings of the first-class carriage of the early morning train.

Earlier biographers have had to work with a mishmash of family legends and romanticised set-pieces, which Hughes qualifies and corrects. Yes, Isabella, the eldest of a combined step-family of 21 children, spent some of her adolescence living in the grandstand on Epsom race-course, but it was by no means unusual for large families of this period to disperse their offspring among sundry relatives and business premises, and it was a temporary arrangement, rather than the fairytale-like banishment it becomes in some accounts. And perhaps Isabella embarked on Household Management because, as her younger sister reported many years later, she couldn't find a good book explaining to brides how to manage their new homes; but it is more likely, given the number of such books already existing, that she and Sam were simply exploiting a lucrative area of the market.

But one family legend, long whispered among Isabella's vast clan of Dorlings and Masons, and hinted at in the previous biographies written by family members, is triumphantly confirmed by Hughes. This is the idea that Sam Beeton had syphilis, and gave it to Isabella on their honeymoon. Piecing together hints in Sam's diaries, the illnesses and deaths of two of Isabella's four children, and the many miscarriages whispered about in Isabella's family, Hughes makes a convincing case, though she perhaps tells us rather too often about the "scrunched and peeling foetuses" typical of the failed pregnancies of syphilitic mothers.

Household Management was by no means the only book of its type published in the mid 19th century. And as many foodies, most notably Elizabeth David and Clarissa Dickson Wright, have pointed out, as a cook book it has nothing on the slightly earlier work of Eliza Acton, from which Mrs Beeton borrowed freely and without acknowledgment. So there is one central question for any one writing on Mrs Beeton: why is it she who is the household name? Hughes deals very effectively with the after-story of Beeton's book, detailing the many spin-off publications and abridged and enlarged versions published by Sam Beeton and later by Ward Lock, to whom he sold the rights in a financially disastrous deal after her death. Both had a vested interest in implying that Mrs Beeton lived on, revising and updating her book, a solid matron, absolutely confident of the right way of doing everything. The illusion was so successful that Cassell, which acquired the rights to the name in 1995, now licenses it to food manufacturers who want to assert the wholesome old-fashioned virtues of their products.

But the initial marketing coup belonged to Beeton herself, the young journalist who so successfully ventriloquised that matronly voice that it continues to reassure us down the centuries, even when most of what Beeton herself wrote, thought and felt is long forgotten.

· Nicola Humble's fully annotated edition of Mrs Beeton's Household Management was published in the Oxford World's Classics series in 2000. Her Culinary Pleasures: Cookbooks and the Transformation of British Food will be published by Faber next month